From the output it's clear that the html directory is still modifiable only by root.

How can I change this in the way that me (non-root) can upload files to the html directory ?

I also tested:

A file's owner can be changed using the chown command. For example, to change the foobar file's owner to tux:

$ sudo chown tux foobar

I typed from the server:

sudo chown mark owner

no effect.

Solution:1

In this case I would leave the directory ownership alone. To modify the permissions for that specific directory so that you can write to it, set read/write permissions, the command being sudo chmod 766 -R /var/www/html. This will assign full permissions 7 for the owner, read/write 6 for the group, and read/write for everyone 6, recursively.

Solution:2

You can make yourself the owner of that directory

sudo chown pi /var/www/html

But you definitely want to set the permissions

chmod 766 -R /var/www/html

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